Yesterday I went to the bi-annual inspection to get a new roadworthy sticker. While the inspection was no problem and I got my new sticker after paying road/weight tax, suddenly the blower fan started to run only on full speed and even was running on full speed when I switched off the blower fan complete on the IHKA control panel.
When I came back home I removed the sword and connected another repaired one on the wire loom without installing it and that worked fine, installed it and blower fan works fine in all speeds.
To remove the 2 screws which hold the sword in place you need a long T20 screwdriver, a small T20 bit is not long enough, as the screws and about 2 cm deep in the casing/hole of the sword. http://www.meeknet.co.uk/e32/BMW_E32...tm_files/9.jpg
Sword and filter removal DIY http://www.bimmerboard.com/forums/posts/54597
Sword repair http://www.bimmerboard.com/forums/posts/355700/http://www.bimmerboard.com/forums/posts/136145/
I have read from some electronic wizzards on the German forum following comments:
Best is to use BUZ11, they can stand more than the original ones.
In case the fan now only switches off while switching off the ignition, then one or several of the MOSFET's in the sword are defective and give permanent signal to run.This has nothing to do with the relay in the sword handle. This relay only activates at "max fan speed" adjustment respect. defects.
The BUZ 74 have 12A and 40 Watt, the BUZ11 have 25-30A and 75 Watt!
To cover the soldered items and protect them against moisture and damages, they either use UHU hard (if you have that in the U.S.), that is a glue which dries quickly,suitable for flexible material and all materials, moisture resistant and heat resistant from -50 to 100 degree celsius. Or any other glue to protect the soldered items. Or a 2-component glue, if you want to make it faster to dry. It should seal all to protect against moisture, that is the most important. And of course it must be resitant against certain temperatures as mentioned above. So any all purpose glue will do probably.

English: Additional info: Heater sword does not stop the blower fan.....This question was aked before several times, why the blower does not stop, although the switch is on "0", here now the solution:

It is a defective Power MOSFET . It has a short circuit.
Test: In the "MAX" position, the fan runs slightly faster than in the control range. This is due to the relay, which bridges the FETs at "MAX". To find the faulty FET, all FETs must be de-soldered and tested as shown in the appendix. With two fingers alternately 1 and 2 (ON) and 1 and 3 (OFF) are touched. It is BUZ71, BUZ11 can also be used. So this error variant can occur on the heater sword too.

comment by demetk: The sword can fail without notice. On my failed sword I replaced the transistors but it still would not power the blower motor. Upon closer examination of the curcuit board I found and fixed some solder joint failures and it finally worked again. You can test for power to blower motor at the sword or at the blower motor. If you have power then suspect the blower motor. I usually apply 12 volts to the blower motor to test if it works.
Here's the locations of the broken solder joints I found,https://i.postimg.cc/nh5s3qk0/sword_2.jpg